Ria; She is angel n.5623....She died 2 years ago in a car accident!! On Earth she had a boyfriend named Ji-Hwan...Every day and Night..she went to the Crystal Ball to see Ji-Hwan!! Ria loves Ji-Hwan so much!! In heaven..all the angels..must forget about their past!! But Ria..she really can`t forget about Ji-Hwan!! One Day....she meet Gabrielle-Nim..(ArcAngel)..When he leaves..Gabrielle-nim..leaves his Death Notes behind!! Ria decided to peek into the book...She was really in shock when she saw Ji-Hwan's name listed in the Death notes book!! She went and begged Gabrielle-nim and Michael-Nim!!Michael-Nim..allowed her to gp to earth but..he gave her 3 conditions!!..From there, her journey on Earth begins.........

From Baka-Updates:
After she died from an accident, Ria become angel No. 5623. She could not forget her life from when she lived. She misses Ban Ji Hwan, her boyfriend on Earth, day and night.
1 year later, Ria happened to see Ji Hwan's name on the death list, the list of every names who is about to die in 100 days. Ria begged high-ranked angels to let her save Ji Hwan. Ria entered the body of So Hae, a shy girl who is tired of her life, the opposite of Ria's personality. Enduring the bullies from step-siblings of So Hae, Ria did her best to bear everything in order to look for Ji Hwan. But when she found him, Ji Hwan cannot recognize Ria...